Title :

Case-control vaccine effectiveness studies: Data collection, analysis and reporting results.

Abstract :

The case-control methodology is frequently used to evaluate vaccine effectiveness
post-licensure. The results of such studies provide important insight into the
level of protection afforded by vaccines in a 'real world' context, and are
commonly used to guide vaccine policy decisions. However, the potential for bias 
and confounding are important limitations to this method, and the results of a
poorly conducted or incorrectly interpreted case-control study can mislead
policies. In 2012, a group of experts met to review recent experience with
case-control studies evaluating vaccine effectiveness; we summarize the
recommendations of that group regarding best practices for data collection,
analysis, and presentation of the results of case-control vaccine effectiveness
studies. Vaccination status is the primary exposure of interest, but can be
challenging to assess accurately and with minimal bias. Investigators should
understand factors associated with vaccination as well as the availability of
documented vaccination status in the study context; case-control studies may not 
be a valid method for evaluating vaccine effectiveness in settings where many
children lack a documented immunization history. To avoid bias, it is essential
to use the same methods and effort gathering vaccination data from cases and
controls. Variables that may confound the association between illness and
vaccination are also important to capture as completely as possible, and where
relevant, adjust for in the analysis according to the analytic plan. In
presenting results from case-control vaccine effectiveness studies, investigators
should describe enrollment among eligible cases and controls as well as the
proportion with no documented vaccine history. Emphasis should be placed on
confidence intervals, rather than point estimates, of vaccine effectiveness.
Case-control studies are a useful approach for evaluating vaccine effectiveness; 
however careful attention must be paid to the collection, analysis and
presentation of the data in order to best inform evidence-based vaccine policies.

Authors :

Verani, J.R., Baqui, A.H., Broome, C.V., Cherian, T., Cohen, C., Farrar, J.L., Feikin, D.R.,
Groome, M.J., Hajjeh, R.A., Johnson, H.L., Madhi, S.A., Mulholland, K., O'Brien, K.L., Parashar,
U.D., Patel, M.M., Rodrigues, L.C., Santosham, M., Scott, J.A., Smith, P.G., Sommerfelt, H., Tate,
J.E., Victor, J.C., Whitney, C.G., Zaidi, A.K., Zell, E.R.

PubMed link :

Journals :

Vaccine. 2017